A curtain wall is an outer covering of a building that spans multiple floors. A curtain wall is non-load bearing in that it does not carry the structural load of the building, other than its own dead weight. As curtain walls are non-load bearing, they may be fabricated from lightweight materials to reduce construction costs. Curtain walls may be designed to keep weather out by resisting air and water infiltration into the building. Furthermore, curtain walls may be designed to accommodate thermal expansion and contraction, and to absorb building sway induced by wind and/or seismic forces. Loads that are imposed on a curtain wall may be transferred to the building through floor anchors that connect the curtain wall to the floor structures of the building.
A curtain wall may be composed of a frame formed from a plurality of horizontal and vertical members. The horizontal and vertical members of the frame may connect to form frame units that receive infill panels of an infill material such as glass, metal, or stone veneer. The vertical members of the frame may be formed from vertical mullions, and the horizontal members of the frame may be formed from transoms or horizontal mullions. The vertical mullions and the horizontal mullions may be formed from a lightweight material, such as extruded aluminum. The vertical and horizontal mullions may assemble with gaskets and pressure plates to create a glazing pocket configured to capture and form a seal with the infill panels. Curtain walls may be characterized as “mullion drained” in which water drainage and ventilation may occur in grooves along the face of the vertical mullions. By contrast, in “zone drained” curtain walls, each infill panel may drain individually so water cannot drain along the lengths of the mullion. In addition, curtain walls may be characterized as “stick” or “unitized” systems. In stick systems, assembly of the frame and glazing (installation of the infill panels) may performed on-site, whereas in unitized systems, frame assembly and glazing is performed at a factory and the fully assembled curtain wall is subsequently erected on the building.
Although current curtain walls are effective, changing practices in building construction are leading to floor structures with deflection limits that are higher than what existing curtain walls may be able to accommodate. For instance, one existing curtain wall design only permits ±2 millimeters of movement, well below the deflection limits of the floor structures of some modern buildings. Other curtain wall systems allow for more movement of the floor structures, but are not widely implemented in practice due to their high costs.
Thus, there is a need for cost-effective curtain wall systems that accommodate the higher deflection limits of the floor structures in some building designs.